The raw materials, such as resin pellets, processed in plasticating barrels are heated by a variety of different methods to obtain a near-liquid or plasticated state. For example, raw materials can be ground and heated before entering the barrel/screw combination for further heating to obtain plastication.
Even when this is done, the primary method of heating the raw material (such as resin pellets) includes the use of either resistance or induction heating of the plasticating barrel itself. Traditionally, the most common method of heating has been resistance heating using contact resistance heaters wrapped around the plasticating barrel.
Because of the high temperatures, severe duty cycles, and difficult environments in which plasticating barrels operate, there are many problems associated with the standard contact resistance heating of plasticating barrels. A discussion of such problems is contained in U.S. Published Patent Application No. 2008/0136066 to Taylor, et al., co-invented by one of the present inventors, having the same assignee, and published Jun. 12, 2008. This publication is incorporated herein by reference in its entirety.
Contact resistance heaters must maintain contact pressure against the barrel, around the barrel circumference and over its length to maintain efficient heat transfer. This is also true of connections between heaters and external power sources. However, the contact pressure can change with age and wear. This produces variable heat transfer resistance between the contact resistance heaters and the barrel, and ultimately non-uniform heat transfer to the barrel. Hot-spots also occur, and further accelerate aging, and eventually may lead to failure of the heating element. Also, non-uniform heating can negatively impact the plasticating process and the quality of the plastic parts, which are produced from the plasticating process.
More recently, wire-ceramic heating systems have been introduced to the plasticating industry. With wire-ceramic heaters, it is important that a secure and reliable connection be formed between wound wire heaters and the external power sources. The connections must not loosen during the plasticating operations. This is necessary to prevent problems when heating the barrel and conducting the overall operation of the plasticating system. It should be noted that the manufacture of resistance wire-ceramic heater layers formed on plasticating barrels can be problematic since it is often difficult to maintain the proper level of tension on the wires during the manufacturing process.
A discussion of this technology is found in U.S. Published Application No. U.S. 2012/0111851, published May 10, 2012, by one of the present inventors and incorporated herein by reference. This application is based upon PCT/U.S. 2010/043062, filed Jul. 23, 2010, and entitled “Method and Apparatus for Providing a Machine Barrel With a Heater.” The disclosed system can serve as a starting point for a wide range of improvements in this art. However, there are certain difficulties inherent to this design so that this design can be improved upon.
The mechanical arrangement of an electrode on a cylindrical plasticating barrel makes external connections difficult under the best of circumstances, and under extreme conditions very problematical. In particular, loosening of the external connections can result in localized high resistances, resulting in localized over-heating, and eventually failure of the electrical connection. Improvements in this technology are needed to ensure a better quality electrical connection between the wound wire and the external (power supply) under all operating circumstances.
One approach to this problem is found in Provisional Patent Application No. 61/509,174, entitled “Thermally Sprayed Electrode for a Ceramic-Wire Heater Layer,” filed Jul. 19, 2011, which includes one of the inventors of the present application. The improvements include the thermal spraying of a metallic band enclosing closely wound electrodes at the end of heater coils, thereby constituting a surface electrode for a connection to external devices. While this constitutes an excellent solution to the aforementioned challenges of connecting external devices to a plasticating barrel, there are still some drawbacks.
In particular, the subject thermal spraying operation is expensive and time-consuming. Further, the thermally sprayed metal band can be improved upon with respect to the mechanical strength provided to the heater windings, and the overall barrel structure. Accordingly, a simpler, more economic, and structurally stronger alternative would be highly desirable.
While the devices contained in the aforementioned published patent publications serve as admirable beginnings for solutions to the aforementioned problems, the current technology admits to yet further improvement. In particular, external connection arrangements for plasticating barrels admit to substantial improvements.
An improved connection system for plasticating barrels would address the aforementioned needs with an arrangement that is more convenient and efficient than existing connection methods. With this improved system, the potential for localized heating due to high current density at an external connection point would be minimized. Further, the improved connection would securely hold and protect the wound heater wire and electrodes under tension, as well as providing means for easier and more reliable attachment of external power connections, in a wide variety of configurations.